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How to build it wrong - basic scratchbuilding and kitbashing techniques

October 2, 2010 - 14:58 — Slambo

So you've built a few structure kits and placed them on the layout. But what do you do when the structure you want on your layout isn't available commercially? Build it anyway. Often, you'll be able to find a structure kit that is almost just like the structure you want or another kit that has a wall or two that would look right. It's times like these that you throw away the instructions and build it wrong!

Tools required

There really aren’t a lot of tools you need, and you’ve probably already got all of these tools anyway. These are the basic tools that you need for kitbashing and scratchbuilding:

Straightedge

Scale rule

Hobby knife with new #11-type blades

Needle files

Sandpaper or emery boards

Squaring jig

Glue - the appropriate type for the material

Basic techniques

Scribe and snap

Use your straightedge and hobby knife to scribe a cutting line in the styrene piece you are working with. Use light pressure and several repeated passes with the knife, but don’t cut all the way through the plastic. When your groove is about halfway through the sheet, stop scribing it. Bend the sheet back and forth on your scribe line until it snaps apart, and use the sandpaper to smooth the edge. Usually, you will not need to smooth the edges when you use this technique on styrene.

Build the walls when they are flat

Cut door and window openings in your walls before you glue them together into a box. It’s much easier to let gravity hold a part against a wall while you are gluing it. Also it’s nearly impossible to get clean window and door openings when you are cutting into a box of styrene (at least I haven’t had much success with it). The best time to add dry transfer signs and lettering is also when the wall is flat against your workbench (but don’t forget to paint them first if you’re adding signs now).

Build L corners and then glue the L corners together

Structures are generally easier to put together when you are gluing an L shape to another L shape. Use your squaring jig to glue two walls together into one of the structure’s corners (the northeast corner, for example). Put together the opposite corner (the southwest corner) while the glue for the first corner is curing. After both L shapes have had a chance to cure on their own, glue the two L corners together to form the structure’s main box shape. I’ve found that I can typically hold this box shape together with one hand for a few minutes while I apply the glue and wait for it to set enough for me to let go.

Bevel the corner joints

Unless the siding on the structure is one that has trim covering the corners, use the sandpaper and files to bevel the corners to a little bit beyond a 45 degree angle. In doing this, you can get the siding right up to the corner without using another piece of .005 (or thinner) material as a wrapper. The square silo in the Tews Cement complex (in the Wisconsin Central project layout [Model Railroader, February 1998, p. 103]) shows how effective this kind of corner can be.

Cut the parts to fit each other

Rather than ensuring that every part is exactly so many scale feet long by so many scale feet wide, only measure the most prominent or the largest of the pieces against the plans. If every piece is measured to be exactly the size of the plans, they likely either won’t fit together or won’t look very good when they are together.

Glue from the inside

Model glues often stain or dissolve the building materials, and if you accidentally apply too much glue, you’re sunk. Liquid cement will flow just enough into the joints by capillary action. So gluing from the inside of the structure will hide any blotches that you create by over application and only enough glue to hold the joint will flow to the outer edge.

Braces are a good thing

Three pieces of plastic glued together are stronger than just the two as they meet at a corner, or even on the same plane. Use a small piece of scrap on the back side of the wall as an extra brace and use it as a common gluing surface to the other two wall pieces. You don’t really need a lot of cross bracing between opposite walls because the roof itself will often act as this bracing.

Cut extra and file

This tip is so simple that it’s scary. Cut pieces slightly larger than they need to be and file them down until they are the correct size. A piece that is too small cannot be easily enlarged (at least not in a way that’s always easy to hide), but a piece that’s too big can always be reduced. Similarly, on door and window openings, cut the hole a little smaller than you need it and file it larger until it’s just right.

Hidden walls don’t need details

Save your time and don’t model a wall that will never be seen. If a structure’s wall will never be visible, and if it’s needed for structural integrity, use blank sheet styrene. If the wall isn’t needed to help with the structure’s strength, leave it out entirely. You will save both the time in not working on that side and money in parts and details that are never added.

Don’t want it seen? Paint it black

This is an old theater trick. If you don’t want someone to see that blank wall that you just added to the back of a structure, paint it black so it doesn’t reflect any light back at the viewer.

Cut from the back

Your first passes in the scribe & snap method mentioned above will rarely be along the exact same line where you want the cut. By making your scribing passes on the back of the material, the front side is unblemished. Also, the scribed lines in the sheet’s face will tend to guide your knife blade, most often in a direction that you don’t want it to go.

Test fit early and often (just like voting)

If you think that you haven’t yet taken off enough material when you are filing, you are probably wrong. Test fit parts immediately after cutting them to find where you need to file or sand. Then after making a few passes with your file or sandpaper, test fit the parts again to make sure that you are taking off the right amount of material in the right place.

Use the lines that are already there

Scribed styrene already has perfectly straight lines so you might as well use them when you need whole numbers of boards. This is the one time where it’s acceptable to cut from the front of the material. However, I’ve found that I almost never need to cut in such evenly spaced increments because the part needs to be just that much larger to fit. Use the lines, but cut much more carefully.

Don’t change a part's placement

Once you have decided where a part will fit, don’t change it. Repeatedly moving parts around on a model will create gaps in places that may not be easy to hide, or the part will be too big, forcing you to file or sand more than you need to. Mark the back side with a pencil so you don’t forget.

Glue long trim and trim to fit

Glue the whole strip of trim material to the model and then trim off the excess. You can always cut off a little more, but you can’t put it back once it’s cut. This goes along the same lines of cutting extra and then filing.